Ischemic stroke results from rapid profound neuron injury and loss of microvascular integrity. The hypotheses to be tested by this Proposal state that during middle cerebral artery occlusion (MCA-O) and reperfusion, i) neuron responses are determined, in part, by the responses to ischemia of the microvessel basal lamina matrix and the nonvascular extracellular matrix (ECM), and ii) blocking specific proteases responsible for these changes in the basal lamina matrix and intercellular ECM will salvage the microvasculature and neurons from ischemic injury. Based upon previous work and preliminary data, we propose that enzymes which degrade matrix heparan sulfate proteoglycans (HSPGs) and heparan sulfates (HSs) are generated following MCA:O, simultaneously with the matrix metalloproteinase pro-MMP-2, and are responsible for microvessel and neuron injury. The goal of this Project is to demonstrate that specific matrix-degrading enzymes play significant roles in microvessel integrity and neuron survival during focal cerebral ischemia. The Specific Aims are to: 1) Localize the post- ischemic expression of proteases that alter matrix-containing HSPGs and heparan sulfates (including select cathepsins and heparanase) in the microvessel matrix, and relate their appearance to pro-MMP-2 expression, basal lamina and intercellular ECM integrity, and to neuron survival;2) Demonstrate that early reperfusion reduces expression of HSPG and HS proteases, and thereby recovers microvessel endothelial cell and astrocyte integrins, basal lamina, intercellular ECM, and neuron integrity;3) Demonstrate that inhibiting HSPG and HS-degrading protease activities can salvage microvessel endothelial cell and astrocyte integrins, basal lamina, intercellular ECM, and neuron integrity;and, 4) Demonstrate that inhibition of MMP-2 or selected cathepsin and heparanase activities decreases matrix HSPG and HS degradation, and reduces the volume of cerebral infarction. Studies of the contributions of HSPG/HS-degrading proteases to the loss of microvessel integrity and neuron injury represent an extension of the ongoing studies of this Proposal, and a new direction in stroke research. They are expected to add substantially to our understanding of the relationships between microvessel matrix and neuron survival in the brain. They also suggest the novel premise that during focal ischemia, neuron injury is mediated in part by changes in specific sensitive matrix components which maintain microvessel integrity and support neuron viability. These studies are likely to lead to new testable therapeutic approaches to preserve mlcrovascular and neuron function which will have relevance to other vascular neuron degenerative disorders.